Reduce port range re-use in tests (#85777) (#85859)

Today we select the port range to use in tests by taking the Gradle
worker ID mod 223. We now use significantly more than 223 Gradle workers
in each test run which means port ranges are re-used, resulting in
spurious failures.

This commit replaces the magic number 223 with a computation defined in
terms of the available ports and the number of ports to allocate per
worker. It also reduces the number of ports per worker to 30 to try and
reduce the frequency of port clashes.

test/framework/src/main/java/org/elasticsearch/test/ESTestCase.java

@@ -193,7 +193,6 @@ public abstract class ESTestCase extends LuceneTestCase {
     private static final AtomicInteger portGenerator = new AtomicInteger();
 
     private static final Collection<String> loggedLeaks = new ArrayList<>();
-    public static final int MIN_PRIVATE_PORT = 13301;
 
     private HeaderWarningAppender headerWarningAppender;
 
@@ -1651,38 +1650,71 @@ public static boolean inFipsJvm() {
         return Boolean.parseBoolean(System.getProperty(FIPS_SYSPROP));
     }
 
+    /*
+     * [NOTE: Port ranges for tests]
+     *
+     * Some tests involve interactions over the localhost interface of the machine running the tests. The tests run concurrently in multiple
+     * JVMs, but all have access to the same network, so there's a risk that different tests will interact with each other in unexpected
+     * ways and trigger spurious failures. Gradle numbers its workers sequentially starting at 1 and each worker can determine its own
+     * identity from the {@link #TEST_WORKER_SYS_PROPERTY} system property. We use this to try and assign disjoint port ranges to each test
+     * worker, avoiding any unexpected interactions, although if we spawn enough test workers then we will wrap around to the beginning
+     * again.
+     */
+
+    /**
+     * Defines the size of the port range assigned to each worker, which must be large enough to supply enough ports to run the tests, but
+     * not so large that we run out of ports. See also [NOTE: Port ranges for tests].
+     */
+    private static final int PORTS_PER_WORKER = 30;
+
+    /**
+     * Defines the minimum port that test workers should use. See also [NOTE: Port ranges for tests].
+     */
+    protected static final int MIN_PRIVATE_PORT = 13301;
+
+    /**
+     * Defines the maximum port that test workers should use. See also [NOTE: Port ranges for tests].
+     */
+    private static final int MAX_PRIVATE_PORT = 36600;
+
+    /**
+     * Wrap around after reaching this worker ID.
+     */
+    private static final int MAX_EFFECTIVE_WORKER_ID = (MAX_PRIVATE_PORT - MIN_PRIVATE_PORT - PORTS_PER_WORKER + 1) / PORTS_PER_WORKER - 1;
+
+    static {
+        assert getWorkerBasePort(MAX_EFFECTIVE_WORKER_ID) + PORTS_PER_WORKER - 1 <= MAX_PRIVATE_PORT;
+    }
+
     /**
-     * Returns a unique port range for this JVM starting from the computed base port
+     * Returns a port range for this JVM according to its Gradle worker ID. See also [NOTE: Port ranges for tests].
      */
     public static String getPortRange() {
-        return getBasePort() + "-" + (getBasePort() + 99); // upper bound is inclusive
-    }
-
-    protected static int getBasePort() {
-        // some tests use MockTransportService to do network based testing. Yet, we run tests in multiple JVMs that means
-        // concurrent tests could claim port that another JVM just released and if that test tries to simulate a disconnect it might
-        // be smart enough to re-connect depending on what is tested. To reduce the risk, since this is very hard to debug we use
-        // a different default port range per JVM unless the incoming settings override it
-        // use a non-default base port otherwise some cluster in this JVM might reuse a port
-
-        // We rely on Gradle implementation details here, the worker IDs are long values incremented by one for the
-        // lifespan of the daemon this means that they can get larger than the allowed port range.
-        // Ephemeral ports on Linux start at 32768 so we modulo to make sure that we don't exceed that.
-        // This is safe as long as we have fewer than 224 Gradle workers running in parallel
-        // See also: https://github.com/elastic/elasticsearch/issues/44134
-        final String workerIdStr = System.getProperty(ESTestCase.TEST_WORKER_SYS_PROPERTY);
-        final int startAt;
+        final var firstPort = getWorkerBasePort();
+        final var lastPort = firstPort + PORTS_PER_WORKER - 1; // upper bound is inclusive
+        assert MIN_PRIVATE_PORT <= firstPort && lastPort <= MAX_PRIVATE_PORT;
+        return firstPort + "-" + lastPort;
+    }
+
+    /**
+     * Returns the start of the port range for this JVM according to its Gradle worker ID. See also [NOTE: Port ranges for tests].
+     */
+    protected static int getWorkerBasePort() {
+        final var workerIdStr = System.getProperty(ESTestCase.TEST_WORKER_SYS_PROPERTY);
         if (workerIdStr == null) {
-            startAt = 0; // IDE
-        } else {
-            // we adjust the gradle worker id with mod so as to not go over the ephemoral port ranges, but gradle continually
-            // increases this value, so the mod can eventually become zero, thus we shift on both sides by 1
-            final long workerId = Long.valueOf(workerIdStr);
-            assert workerId >= 1 : "Non positive gradle worker id: " + workerIdStr;
-            startAt = Math.floorMod(workerId - 1, 223) + 1;
+            // running in IDE
+            return MIN_PRIVATE_PORT;
         }
-        assert startAt >= 0 : "Unexpected test worker Id, resulting port range would be negative";
-        return MIN_PRIVATE_PORT + (startAt * 100);
+
+        final var workerId = Integer.parseInt(workerIdStr);
+        assert workerId >= 1 : "Non positive gradle worker id: " + workerIdStr;
+        return getWorkerBasePort(workerId % (MAX_EFFECTIVE_WORKER_ID + 1));
+    }
+
+    private static int getWorkerBasePort(int effectiveWorkerId) {
+        assert 0 <= effectiveWorkerId && effectiveWorkerId <= MAX_EFFECTIVE_WORKER_ID;
+        // the range [MIN_PRIVATE_PORT, MIN_PRIVATE_PORT+PORTS_PER_WORKER) is only for running outside of Gradle
+        return MIN_PRIVATE_PORT + PORTS_PER_WORKER + effectiveWorkerId * PORTS_PER_WORKER;
     }
 
     protected static InetAddress randomIp(boolean v4) {

test/framework/src/test/java/org/elasticsearch/test/test/ESTestCaseTests.java

@@ -183,12 +183,12 @@ public void testWorkerSystemProperty() {
     public void testBasePortGradle() {
         assumeTrue("requires running tests with Gradle", System.getProperty("tests.gradle") != null);
         // Gradle worker IDs are 1 based
-        assertNotEquals(10300, ESTestCase.getBasePort());
+        assertNotEquals(ESTestCase.MIN_PRIVATE_PORT, ESTestCase.getWorkerBasePort());
     }
 
     public void testBasePortIDE() {
         assumeTrue("requires running tests without Gradle", System.getProperty("tests.gradle") == null);
-        assertEquals(10300, ESTestCase.getBasePort());
+        assertEquals(ESTestCase.MIN_PRIVATE_PORT, ESTestCase.getWorkerBasePort());
     }
 
     public void testRandomDateFormatterPattern() {